Similarity in the Modeling of Cable Twisting and Looping

O armored cable generates a twist moment under tension. An assembly of armored and armorless cables therefore represents a twist moment and twist deformation problem as well as a tension problem. Under certain conditions involving moment and tension, a section of cable may relieve twist by looping. If the yield stress of the armor wires is exceeded by subsequent pulling of a looped section, a kink will result. In the installation of communications cables in deep water, the twist properties of the coaxial cable are important. ] Excessive twist deformation can produce cable failure. Kinks in cable make recovery difficult or impossible. Model tests which duplicate the full-scale installation appear attractive for making comparisons of different laying schemes and determining the conditions under which looping and fouling are likely. In order for model tests to be valid, certain conditions must be satisfied by the model. These conditions are embodied in the dimensionless similarity parameters, which must have the same value in the model as in the full-scale operation. In Ref. 2, the similarity parameters were worked out for cases in which twist, bending, looping, and kinking are not important. More precisely, the shear forces associated with twist and bending are small compared to the tension. Only cable weight and tangential and normal drag appear in the equilibrium equations. This is the case for most cable configuration problems. The additional considerations lead to more terms in the equations defining the configurations, and hence to ad-